Electrical control device



Aug- 2, y1949. J. YoUHoUsE 2,477,845

ELECTRICAL CONTROL DEVICE Filed Feb. l2, 1947 2 Shee'ts-Sheet l INVENTOR. y Jose/072, You/zo we 67dl 57C BY ATTORNEYS# Aug. 2, 1949. J. YouHoUsE l 2,477,845

ELECTRICAL CCNTRCJ DEVICE Filed Feb. l2, 1947 2 Sheets-Sheet 2 g2 HZ INVENTOR. /w'epb You ha 11.5@

ATTORNEXj Patented` Aug. 2, 194g UNITED STATES PATENT GFFICE ELECTRICAL CONTROL DEVICE Application February 12, 1947, Serial No. 728,107

17 Claims.

This invention relates to adjustable electric heating devices, especially devices such as heating pads and the like, having controls providing for a plurality of heat adjustments in such devices.

The invention is concerned with improvements in the devices of my Patent Number 2,415,858 entitled Switch device and copending patent application Serial Number 721,979, led January 14, 1947, entitled Rheostatf An object of the invention is to provide in a heating pad an improved small and compact resistor-type control device the casing or housing of which has a cooler operating temperature than was heretofore obtained, thereby eliminating the necessity for separate heat-insulating plates on the casing exterior, or similar insulating instrumentalities previously required.

In small, compact resistor-type control devices of the type referred to, a resistor element is located within the casing of the device, which casing is formed of molded insulating material. The resistor, for reasons of economy of space and convenience of mounting and assembly, is presstted and carried in a recess molded in the inner surface of the exterior wall of the casing. In the past, the recess was made to closely t and conform to the resistor element and during the normal operation of the device, the element became quite hot and imparted its heat to the casing wall, in addition to other ways, by direct contact therewith. The heat exchange between the resistor element and the casing wall was quite efficient, and as a result the wall of the casing became hot to the touch, and a user if he noticed this Would be likely to think that the control device was operating improperly, or that a dangerous condition was developing.

To offset the effect of this, in the past, a heatinsulating plate was provided to cover the portion of the casing which evidenced the most heat, the plate being made as ornamental as possible under the circumstances. While this in general proved to be satisfactory in reducing the heat which a user telt, it represented an added expense and detracted to an extent from the appearance of the control device.

According to the present invention an improved mounting is provided for the resistor element of the control device, which results in a much less eicient heat exchange between said element and the wall of the casing, thereby resulting in the casing having a cooler operating temperature and doing away with the need for an exterior heatinsulating plate. In accomplishing this, the resistor element is so mounted that an appreciable air space exists between it and the interior surface of the casing wall, the said space eliminating heat exchange through direct conduction and reducing considerably heat exchange by radiation. I have found that by providing a space in the neighborhood of or so, the heat exchange is so reduced that the exterior of the casing is not unduly warm to the touch and therefore it is not necessary to employ any auxiliary heat-insulating device, such as the external heat-insulating plate mentioned above.

Another object of the invention is to provide an improved contact organization, in a small and compact control device of the above type, which eliminates the possibility, heretofore present, of the resistor element of the device being inadvertently connected in the circuit to carry the whole current thereof and therefore become overheated, should the proportions of the component parts of the devices vary slightly due to departure from manufacturing tolerances, etc.

In the control devices of my patent and application above referred to, the circuit control was effected by a pair of electrically connected switch blades extending in opposite directions and respectively engaging, on the one hand a metal contact segment, and on the other hand the resistor element of the device. It was intended that the switch blades engage the contact segment and the resistor element substantially simultaneously when actuating the device from off to low" position, or that the contact segment be engaged slightly ahead of the resistor element. However, due to manufacturing variations in the dimensions of the various cooperable parts, it sometimes happened that the resistor element was engaged prior to engagement of the contact segment, and the control device left in this condition. As a result, the resistor element carried the entire current through the device, which it was not designed for, and therefore became unduly overheated. In these prior control devices the contact between the switch blades and the resistor element was established through a metal retainer finger which was located to overlie one end of the element and hold the latter in position in the casing of the device.

According to the present invention the above diiiculty is overcome without increasing the size of the control device or adversely affecting the range of heats of the pad by a novel organization wherein the metal retainer nger is insulated from the resistor element so that even if the linger should be contacted first, before contact is established to the metal contact segment, no current will flow solely through the resistor element and therefore the latter will not become overheated. In addition to eliminating the possibility of overheating of the resistor element, the insulating of the retainer finger results in a new, very low heat setting for the heatingrpad, and in effect extends the range of adjustment thereof.

As the contact blades of the improved control device are advanced from off to the starting low position, contact is positively established between one blade and the contact segment before the other blade leaves a retainer linger for the resistor element, and therefore there is positive assurance that at no time will the resistor element be made to carry the entire current through the control device.

For the starting low position of the switch blades, due to current being conducted from the latter solely7 through the contact segment because of the insulation of the retainer finger for the resistance element, the entire current through the control device will be caused to flow through the thermostat heater in the heating pad, and this will cause a high rate of activity of the thermostat and a consequent very low temperature in the pad, which very low temperature I term a low-low heat.

Another object of the invention is to provide an improved contactor assembly which is ar ranged for quick and economical assembling of the component parts, and is so constructed that when once assembled the parts constitute a unit and are not separable from each other to cause diiiiculty Vwhen mounting the assembly in the casing of the control device- In the devices of my above-referred-to patent and application, the contact assembly comprised a rotatable member having a spindle and a manually engageable actuating wheel, and comprised oppositely extended switch blades associated with the wheel and spring urged therefrom by a helical compression spring. In this assembly the switch blades were not permanently fastened to the actuating wheel and at times difficulty was experienced in holding the switch blades and spring to the wheel while the assembly was installed in the casing of the device.

According to the present invention this difculty is overcome by the provision of an improved switch blade structure wherein hooked deformable arms are provided for cooperation with shoulders on the actuating wheel of the assembly, the arms being so arranged that when the switch blades and actuating wheel are brought together under pressure the arms will be deformed and hook themselves over the shoulders of the wheel thereby to permanently retain the switch blades on the wheel. As a result, the contactor assembly remains as a unit, the component parts of the assembly being permanently secured in place. This improved assembly may be installed in the casing of the control device quickly and without diiiculty, thereby reducing the assembly costs of the device.

Other features and advantages will hereinafter appear.

In the accompanying drawings:

Figure 1 is a plain view of a control device made in accordance with the invention.

Fig. 2 is a similar view of the control device, but with the cover removed.

Fig. 3 is an axial section of the control device taken on the line 3 3 of Fig. 1.

Fig. V4 is a transverse section of the device taken on the line 4 4 of Fig. 2, but with the cover in place.

Fig. 5 is an exploded view of the contactor assembly of the control device, illustrating the method of assembly of the component parts, and the tools used in such assembly.

Fig, 6 is a view like Fig. 5, but with the parts of the assembly brought together just prior to their being permanently joined.

Fig. 7 is an end view of the assembled contactor assembly.

Fig. 8 is a perspective view of the contactor of the assembly prior to attachment to the actuating wheel, and

Fig. 9 is a schematic diagram of the control device and a heating pad controlled thereby.

The control device of the present invention as shown includes a casing 12l) which may be conveniently manufactured of molded plastic. The casing 2d when assembled is of elongate shape having tapered ends and a substantially oblong central transverse cross-section. It is separable into two parts 26a and Zlib along a substantially axial plane parallel to its broader lateral surface. r.The two parts are held together by means of screws 2i adjacent opposite ends of the casing, and at each end the edges of the casing parts are recessed to provide apertures 22 and 23 (when the two halves are assembled) to receive conductors extending into the interior of the control device.

Approximately at the center lof the two casing halves 20a and Zeb, their opposite lateral edges are recessed to form a pair of longitudinal slots 2li when the casing is assembled, through which an adjustment disk 25 carried within the casing may extend. The casing portion Zlib is also provided with a sight opening or aperture 26 for observing a visual indicator or dial 27a. The sight opening 2t preferably has a central arrow tip 26a at one side thereof for cooperation with the dial 21a to provide a Vreference point thereof.

A pair of conductors 28 entering the casing 2D through the aperture 22 thereof is adapted to connect the control device with a source of electric power. The ends of these conductors extend through grooves 29 in the interior of the casing on opposite sides thereof and are connected to a pair of terminal screws 3i! and 3| carried by a web 32 formed in the casing half 29a. A web 33 is also formed in the central wall of the casing half 26a and comprises a semi-circular portion 33a adjacent the web 32 and an oblong portion 33h extending toward the opposite end of the casing. The breadth of the oblong portions 335 of the web 33 is such as to allow for a pair of clearance grooves 34 and 35 which extend between the said portions and the lateral casing walls to receive connectors ley-passing the said web.

A central recess 36 substantially at the Center of the casing half 2da is formed in the web 33 with an annular bearing surface 37 surrounding a central spindle-receiving cavity or bearing 38 at its base. The opposite half 2Gb of the casing is provided with a similar bearing cavity 39 disposed directly opposite cavity 38, said cavities receiving the ends of a spindle it serving as the shaft for the indicator dial 21a. and the adjustment disk 25. The translucent dial Z'lc is attached to a collar il on the upper end of the spindle Il@ adjacent the bearing 39, and a portion of its surface extends under the sight opening 25 which is offset from the axis of the spindle.

stance of molded plastic material and is of generally circular shape. It comprises a hub 42 molded on spindle 45 on the opposite side of the disk from collar 4l, its lower surface forming an abutment to engage the bearing surface 31. The peripheral edges of the disk 25 extend through the lateral slots 24, so that the protruding arcuate portions of the said disk are available for its manipulation.

i The portion 55h of web .33 has a transverse slot 45 therein, adjacent the circular recess 36, for receiving connector or resistor means, and beyond the slot two screws 45 and 48 are threaded into the web. An elevated portion of the web 33 beyond slot 45 forms an additional web 49, which carries a pair of terminal screws 55 and 5l adjacent end aperture 23. As indicated in Fig. 2, the three conductors 55a, 52h and 52o are connected to terminal screws 50, 5I and 48, respectively. rThese conductors are adapted to connect the control device to a device such as a heating pad to be controlled.

Terminal is connected directly to terminal 5l by means of an insulated conductor 53 which lies in lateral groove 35 of the casing part Eea.. Terminal Si carries a resilient conductor strip or spring contact 5d which extends through lateral groove 34 of casing part 28a to a point opposite the spindle 45 or its bearing 38. An angular tip 55 on the spring contact 54 extends inward into the circular recess S5 through a radial groove or slot 56 in the side of the web 33, terminating just short of the hub 42. The spring contact 54 is mounted so that its resilience normally urges its tip 55 toward the top of the slot 55 in Web 33.

A metal contactor 51, Fig. 8, comprises a circular cupHshaped portion 51a having a central aperture in its base adapted to receive the hub 42 of spindle 453, and comprises a pair of diI ametrically opposite radial blades or wings 51h, each having a pair of folded lateral flanges or arms 51o. The exposed surface of each of the wings 51h is convex. rEhe arms 51C are adapted to engage the edges of a pair of correspondingly disposed apertures 58 in the adjusting disk 25 so that the disk 25 and contactor 51, when assembled as illustrated in Figs. 3, 6 and '1, are coupled for mutual rotation.

A coiled compression spring 59 surrounds hub 42 and is supported at one end against the face of the disk 25. The opposite end of the spring 5s bears upon the base of the cup-shaped portion 51a of contactor 51. Thus, when the control device is assembled, spring 59 urges the contactor 51 toward the wall of the casing half Zea, and presses wings 51h toward the upper surface of web 33, Fig. 3, while the arms 5ic thereof engage the apertures 5S in the disk so that the contactor is rotatable thereby.

According to the present invention the contactor 51 is so arranged that it may be easily and quickly permanently assembled to the adjustment disk 25 so that these may be handled as a unit, thereby facilitating their assembly into the cas ing 25, and facilitating the assembly of the entire control device. In accomplishing this the arms 51o of the contactor 51 terminate in hooks 51d which extend inwardly in pairs, toward each other, and the webs 51o, as may be clearly seen in Figs. 5 and 6, extend at an angle with respect to the end surface of the cup-shaped portion 51a. The arrangement is such, referring to Figs. 5 and 6, that the hooked arms 51o may be extended through the openings 58 in the adjustment disk 25 by bringing the disk and the contactor 51 axially together. Prior to such movement, of course, the spring 59 is interposed so as to be positioned on the hub 42 of the disk. After bringing together the contactor 51 and adjustment disk 25, further pressure on the wings 51h will cause these to become straightened and aligned with each other, and in so doing the hooked arms 5c will be swung inwardly toward each other causing the hooks 51d thereof to overlie the shoulder' or end of the hub 42 of the disk for engagement therewith. It vwill be seen that upon this deforming pressure being removed, the expansion of the coil spring 59d will cause the hooks 51d to be held in engagement with the hub 42 of the adjustment disk. Thus the contactor 51 is now permanentiy attached to the disk and cannot inadvertently be separated therefrom.

Preferably the contactor 51 is assembled to the adjustment disk 25 by the use of tools 25a and 51e, as shown in Figs. 5 and 6, thes-e tools being adaptable for use in a light punch press such as a foot or kick press, and enabling the operation of assembling thc contactor to the disk to be quickly and economically carried out. Such assembly is preferably done prior to assembly of the translucent dial 21a. to the spindle 45.

The tip 55 of resilient spring contact 54 is positioned beneath the lower surface of the cupshaped portion 51a, of the contactor and by virtue of its resilience, yieldably engages said contactor forming a continuous electric contact therewith in angular positions of the contactor.

The upper surface of web 33 is provided with a pair of integral raised portions Gt on opposite sides of the recess 35, having concave upper surfaces forming projections adapted to serve as insulating detents for yieldably holding the wings 51h of contactor 51 positioned transversely of the casing 2li. One of these raised detente is split, as shown by the slot 56 through which the tip 55 of spring contact 54 extends.

The resistor element of the control device is in the form of a resistance coil which comn prises resistance wire wound around an insulating core 86, the element being press-fitted in the slot 45 of the casing half 20a.

In accordance with the invention only the sides of the slot 45 are made to engage and closely fit the resistor element of the control device, the bottom of the slot being spaced an appreciable distance from the element as shown in Figs. 3 and 4, except at the slot ends where the bottom is raised to engage the ends of the insulating core 86, By this construction an air space is provided between the outside wall of the casing half 2da and the resistance coil 85 of the resistor element, and I have found that a relatively small air space of 11e or so is suicient to eifectively reduce heat exchange between the outer wall of the casing half and the resistor element, eliminating `heat by conduction and greatly reducing heat by radiation. As a consequence, during the normal operm ation of the control device the heat which is prcs ent in the resistance coil 85 does not produce a distinctly noticeable hot spot in the exterior wall of the casing half 20a as was heretofore the case. By this construction, therefore, there is obviated the need for any shields or other insulating plates on the exterior of the casing half 20a. to prevent a user from noticing the heat of the control device.

The terminals 46 and 48 carry a pair of metal conductive clips or retainers 81 and 88 which extend toward the recess 35 and have narrowed contact surfaces as shown in Fig. 2 for engagement with the wings.- SE1-'b orthecontacter 51:. The clips 8:1 and 8.81. oizerlie` andare clamped against the Opposite ends of the. resistance coil 85. The narrowed contact stu-faces of the clips. 8:1 and 83 are preferably flat; so. that they do not act as detents whenengaging the Wings 51h of*- the contactor 51. A flat; metal segment or sector contact 89 is provided to,t extend arcuately around the side ofthe recess 36 opposite the slot, 4.5, the said contactor being anchored by a terminall screw 61. and overlyingthe arcuate portion of the web 33 and tere minati-ng adjacent the raised insulating detents l() or said web.

According to the present; invention only one. of the clips 81 and 88,v namely the latter, is made tov form electrical contact withV the resistance coil. 85'. 'Irhemeta-1 clip: 81,-, however, is insulated. from the resistance coil 85 by the nlQv-ision of a thin insulating strip` 81a, which maybe of ber orthe like, and. which is interposed between the clip andl the resistance coil.

lhegstructure of; the control device is such that it is intended,A when shifting the adjustment disk 2,5 from off to the starting low position, that the Wings 51:13. of' they contactor 51 simultaneously engaga onv the one hand the contact segment 89, and on the; other hand; the retainer finger or clip 81. Heretolore this. clip S1 was not insulatedfrom the.- resistance coil; 85, but formed an electrical connection` thereto. Due to Variations in the dimensiQIlS and tolerances of the various component parts of the control device, have found that the one web 51h. of the contacter 51 may be caused to` engage the retainer clip 31 Without the opposite web 51h engaging the` contact segment 8.8, and in the past this has resulted in` an unde- Y sirable condition in that allvof the current through the control device was made to nass` through the resistance coil 35, producing excessive heating of the latter andv resulting in an undesirable condidition.. However, by the interposition of the inn sulating strip 81a so as to-insulatetheclip. 81. from the resistancev coil B5., this situation is prevented from, occurring., since by the time thatrone web 52bhas. engaged. the rst convolutions. of the resistallce coil 85 adjacent the clip 81, the other web 516 will surely be in engagement with ythe Contact segmentv 8,9. Of course, `during the time. that the clip. 8J is beine. engagedby the. one web 5.119v nol current can flow. throughthe resistance coil 85@v due tov the. insulationbetween the clip and coil 85., and there is thus obi/lated a condition which was. potentially dangerous.

The. dial 211i has words designating the position or theswitch and also eraduatedscales extending: over arcs which corresnond with the energizing adjustment ranges, said; scales having numerical indicia which increase from low to high. All of the indicia on; the dial 21aA are consecutively` visiblein. the sight opening 2.6, as shown in Eig. 1.,'. when the;- wheel 25 is turned.

To. complete the connections of the control de vice, terminal screw 61 is connected, byv a conductor o r bus bar to terminal. screw 55,4 and hence'to conductor 52a.

As a resultI of the aboveconstruction, contacter 5.1 when rotated by dist 2/5 out oi its o, insulated datent-engaging position the.` casi g torn-1S a. bridge between sectorV contact, 89 andV `various points; on they resistance coill 85, or its trol-led thereby is; Eig. a.. The heating; had here comprises a mainheatingr cnil 92 with apair`4 of; safety/devices -lhsuciiA as, fuses. or thermos-tats Qpreferably the;4 latter): included in; its. circuit. @ne end of the main heating coil 9%2; is. connecnedy to terminal 5| by conductor 5211-,` and thence through conductor 5 3.l to inputgterminal, 30: and` conductor 28.-. The opposite. endl of the coil 92 is connected in series with a normally closed. bimetal switch 9.4. The latter is. connected through a. pair ci parallel. circuits to the other. input terminal al and its associated conductor 28.

Qne of these'. circuits traverses conductor 52e to terminal 48. and its associated clip 88. at. one of the resistance coil 8.5, then through. the turns of; the latter coill includedbetween clin 88. and.. contacter 51, and nal-lythrough the latter andsprine contact4 5.4;-55 to input terminal 3 I..

The other paralleli circuit from the.r bimetal switch- 94 to terminal 3i includes an auxiliary. heating coil 95; in theY heating pad, which is, connected by conductor 52a to terminall 5t, From the latter, it traverses bus bar sector contact 89' and contacter 51, rejoining the rstfdescrib'ed cir-` chit at` spring contact 5ll--55.,l carriedv by input terminal 3i.

The auxiliary heating coil. 95 is adapted, either alone, or in conjunction with the main heating coil Q2, to control the, temperature,y and. hence the operation, of the bimetallic-switch 94'. When the temperature ofV the; loi-metallic switch 94. iS. sunicienly raised by theheatgenerated in coil. 9.5., possibly sunnlemented by that generated in coil S32, switch. 954 opens, interrupting the, circuit.

kr through coii @2f as. wellA as: the aforesaid vparallel circuits. On cooling sufficiently, the binietallic, switch anton-lati.callyA reclusos and.A reestablishes the circuits.

lt will be. observed that ccntactor 51. uponclockwiseV rotation from the position in, which it. engages insulated. cle-tent 6i!A initially engages clip. 81 at one endI of the, resistor coil 55 and simultaneously, sector Contact 83,. Referring to. the wiring diagram of Fig. 9, it will be. seen that nov current will flowv trom. the contacter 51Y and retainer iinger or clip 8.1 to the resistance coil. 85,v since the latter and clip. are insulated fromeach other. Instead, current flows from the contacter 5? to the contact segment 89 and thencel through the Wire 1.0, terminal 5,9, wire `52a to the thermostat heater 95,. Eromhere current flows through thev thermostat 94, heating element. 92,y safety thermostats 9.3 and back through the return. Wires 52h and 53 to the other currentsupplxt Wire This connection causes: a maximum heating ot the thermostat heater 95. and therefore results, in a maximum activity ot the thermostat, causing an extremely low heat4 in the heating element s2 of the heating pad, and this. extremely low.y heatl term a low-low" heat.

Upon. continued clockwise movement. of` the Contacter 5,1. it will, while remaining in engagement with sector contact 89, leave the retainer. clipf 8.1 and engage the firstl few: convolutions ci. the resistance. coil` 8.5. For this. position, the current which passes through the thermostat heater. 95 is, also byepassed through. the resistance. coil 85, resultingin; a lesser heat in the thermostat, heater 95 and, less activity ot the, thermostat 94. Asa conseeruence the heating element 9% o f the; heating pad Willi bey maintained at. .al 'ti/armer temperature, their the lowdow heat mentioned. above.j and this. warmertem-perature I term. low, since it is analogous: to the usual low. heat. encountered.

in heating pads. Upon continued clockwise movement, contactor l, while remaining in en gagement with sector contact 89, moves across the coil 85 including progressively fewer and fewer turns of the resistance 85 in parallel with the auxiliary heating coil 55. Finally, it reaches clip 88 at the opposite end of said resistance coil. At this point, the resistance 85 no longer remains in the circuit, while auxiliary coil 95 is shunted, and the full line voltage is impressed across the terminals of the heating coil 92.

Variations and modications may be made within the scope of this invention and portions of the improvements may be used without others.

I claim:

1. A control rheostat for connection into the cord of a heating pad or the like, comprising a hollow casing formed of insulating material and adapted to be held in the hand; and electrical control means in the casing, including a heatable and heat-dissipating resistor separated from the outer wall of the casing overlying the same by an appreciable air space to minimize heat exchange between the resistor and casing wall whereby the latter adjacent the resistor is maintained relatively cool during normal heating of the resistor.

2. A control rheostat for connection into the cord of a heating pad or the like, comprising a hollow casing formed of insulating material and adapted to be held in the hand; and electrical control means in said casing, including an elongate heatable and heat-dissipating resistor secured at its ends to the casing, said resistor intermediate said ends being separated from the outer casing wall overlying the same by an appreciable air space to minimize heat exchange between the resistor and casing wall whereby the latter adjacent the resistor is maintained relatively cool during normal heating of the resistor.

3. A control rheostat for connection to the cord of a heating pad or the like, comprising a hollow casing formed of insulating material and adapted to be held in the hand; and electrical control means including a resistance coil and a heat-insulating core on which said coil is wound, said core being secured to the casing and said coil being separated from the wall of the casing overlying the same by an appreciable air space to minimize heat exchange between the coil and casing wall whereby the latter adjacent the coil is maintained relatively cool during normal heating of the resistor.

4. A control rheostat for connection into the cord of a heating pad or the like, comprising a hollow casing formed of insulating material and adapted to be held in the hand; and electrical control means including an elongate resistance element comprising a resistance coil wound on and between the ends oi an elongate heat-insulating core, said core at its ends being secured to the casing and said coil being separated from the wall of the casing overlying the same by an appreciable air space to minimize heat exchange between the coil and casing wall whereby the latter adjacent the coil is maintained relatively cool during normal heating of the coil.

5. A control rheostat ior connection into the cord of a heating pad or the like, comprising a hollow casing formed of insulating material and adapted to be held in the hand, said casing having at least one generally iiat hand-engaging outer surface and a relatively thin wall at said surface; and electrical control means including an elongate heatable and heat-dissipating resistor mounted in the casing with its side adjacent the said thin wall and separated therefrom by an appreciable air space to minimize heat exchange between the resistor and thin wall whereby the said exterior flat surface of the casing is maintained relatively cool during normal heating of the resistor.

6. A rheostat comprising a supporting body; a manually operable member rotatable on the body and having a pair of electrically connected contact arms extending from it in opposite directions; a metal contact segment extending along one side of the rotatable member, said segment being engageable by one of the contact arms; an elongate resistance element extending along the other side of the rotatable member, and engageable by the other contact arm; and means for securthe resistance element to the body, including a metal retainer finger overlying one end of said element, said linger being engageable by said other contact arm substantially simultaneously with engagement between the one arm and said segment, and said iinger being insulated from said resistance element.

7. A rheostat comprising a supporting body; a manually operable member rotatable on the bodi7 and having a pair of electrically connected contact arms extending from it in opposite directions; a metal contact segment extending along one side of the rotatable member said segment being engageable by one of the contact arms; an elongate resistance element extending along the other side of the rotatable member and engageable by the other contact arm; and a pair of metal retainer fingers for the resistance element, said i-lngers overlying the ends of the element and being engageable by said other contact arm substantially simultaneously with engagement between the one armand said segment, and one of said ngers being insulated from said resistance element.

8. A rheostat comprising a supporting body; a manually operable member rotatable on the body and having a pair of electrically connected contact arms extending from it in opposite directions; a metal contact segment extending along f one side of the rotatable member and engageable by one of the contact arms; an elongate resistance element extending along the other side of the rotatable member and engageable by the other contact arm; means for securing the resistance element to the body, including a metal retainer nger overlying one end of said element and engageable by said other contact arm substantially simultaneously with engagement be tween the one arm and said segment; and a thin strip of insulating material interposed between said nger and resistance element to insulate the latter from the finger.

9. A rheostat comprising a body of insulating material; a manually operable member rotatable on the body and having a pair of electrically connccted contact arms extending from it in opposite directions and yieldable thereon, said body having pairs of integral, spaced projectionsk on opposite sides of the rotatable member, said pro'- jections being traversable by the contact arms and providing detents for said arms; a metal contact segment extending along one side of the rotatable member and between the pairs of projections oi the body, said segment being engageable by one of the contact arms; an elongate resistance element extending along the other side of the rotatable member between the pairs of projections of the body, said element being engage- '11 able `bythe other vof the contact arms; and a pair of metall `retainer fingers for Vthe resistance ele--v ment, loca-ted respectivels7 adiacent correspondu ing projections Aof the 'said pai-rs, said retainer fingers overlying the ends 'of the resistor element ,5 andbeing individually :engageable by one of said Contact arms substantially simultaneously with engagement `between theother arm and :said seg-- ment, and one of said ngers beingfinsulated-from said resistance element.

In aiheating device, a thermostatic switch; a heater for Vthe thermostatic switch; a support-- ingibody; -a -manua-lily operable member rotatable on the body and having a pair of contact arms electrically rconnected together and extending from it Ain opposite directions; a metal contact segment 4extending along one side of the rotatable member, said segment being engageable by oneor'the other .of the contact arms and being connected with one point of said heater; a resistor extend-ing along the other side of the rotatable member, said resistor being engageable by one or the other of the contact arms and having one point connected with another :point of said heater; means -for securing the resister to the bod-y, including a metal retainer nger overlying one end of said resistor, said finger being en gasea-ble -by either of said contact arms sub-stanftia'lly simultaneously with engagement between the other arm `and said segment, and said finger being insulated from said resistor; a pair of eurrent supply wires, one of said wires being con nected with said contact arms; and electric heatingfmeans connected with theeonnection between the resistor `and heater, and connected with the other current supply wire, the said thermost t switchl being connected for controlling the circuit of said heating means.

1i. In a heating device, a thermostatic switch: a heater 'for the thermos-tatie switch; a supprnt ing body; a manually operable member movable on the `body and having a pair of contact arms electrically connected together and extending from it generally in opposite directions: a metal contact plate extending yalong one side of the movable member, said pl-ate being engageable by one of the contact arms and being connected with one poi-nt of said heater; a resistor extending along the other side of themovable member, said resistor being engageable by the other of the corrtacts arms and having one end connected with another point of said heater: means for securing the resistor to the body including a metal retainer1 finger overlying the unconnected end of r sistor, said finger bei-ng engageable by said other contact arm substantially simultaneously withVv engagement between the one arm and said plate and said -nger being insulated from said resistor: a pair of current supply wires, one of said wires being connected with said contact and electric heating means connected with the connection between the resistor and heater and connected with the other current supply wire, the said thermostatic switch being connected for controlling the circuit of said heating means,

12. A switch contacter assembly comprising a rotatable member Y having a manually engageable portion, and having extending transversely of its axis a pair of shoulders located on oppositev sides of sa-d axis; a switch blade; means guiding 70 the switch blade o-n the member for axial movement; and stop means preventing removal of the blade from the member in one axial direction, said 1:2 bla-de Thai/ing a `pair of 'opposite'ly :located :hooks engaging said shoulder and preventing removal .of the Iblade from the member in the vother axial direction.

13. A switch :contacter vassembly comprising a manually engageable wheel having a pair oi openings through it .from one side to the other, said openings 'being Von opposite sides :of the wheel axis; and a switch blade extending across one side of the wheel and having a pair of hooked arms extending through Vthe openings in the wheel and engaging the other side of the latter for preventing removal of the blade rfrom the wheel.

14. A switch contactor assembly comprising a manually engageable wheel having a pair of openings through it irom one side to the other, said openings being on opposite sides of the wheel axis; a switch blade extending across one side of the wheel and'havlng a pair of hooked arms extending through'the openings in the wheel and engaging the other side .of the latter for preventing removal of the blade from the wheel; and a spring urging the `bla-de 'away from the one side of the wheel and urging the hooked arms toward engagement with :the .other side of the wheel.

l5. A switch contactor assembly comprising a rotatable plate having a :pair of .openings through it from one side to the other, :said openings being on opposite sides of the 'plate axis; and a switch blade extending across one side of the plateand having a pair of hooked arms extending'thrnugh the openings in the plate .and engaging the other side of the latter for preventing removal of the blade from Vthe plate.

it. The method of assembling a rotary switch blade member having a pair oi oppositely located deformable hooked arms to a rotary actuating member having opposite :shoulders adapted fior cooperabl-e engagement with said arms, which includes the steps of 'bringing `the said members axially together to locate the arms adjacent the cooperable shoulders, and then forcing the members axially toward each other to apply a deforming pressure on the arms and cause the latter to shift into engageable position with respect to said shoulders, thereby preventing separation of the members.

17. The method of assembling a rotary switch blade member having a pair of oppositely located deformable hooked arms to a rotary actuating member having opposite shoulders adapted for cooperable engagement with said arms, which includes the steps of bringing the said members axially together to locate the arms adjacent the coopcrablc shoulders, backing up the ksaid members with tools, and applying pressures to the tools to force the mem-bers axially together and deform the arms to cause the latter to shift for engagement with said shoulders so as to prevent separation of the members.

JOSEPH YOUHOUSE.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,938,396 Megow Dec. 5, 1933 2,151,037 Krieger Mar. 21, 1939 2,172,634 Axtell Sept. 12, 1939 2,177,291 Schellenger Oct. 24, 1939 

